4 
A. D. Darbishire. 
one x-chromosome in the reducing division ; hence the mature 
ovum contains c -f x chromosomes, for the germ and somatic cells 
are alike in chromosome characters. It is therefore a just 
inference that the following combinations have occurred :— 
Sperms. Ova. Zygote. Sex. 
c or (c + y) + (c + x) = (2 c + x) or (2 c -f x + y) $ 
(c + y) + (c + x) = (2 c + 2 x) 2 
(ef. Diagram in Fig 4). 
Hence it follows that the sperms carrying the x-element are 
female-producing, whilst the sperms without the x-element or with 
the y-element are male-producing. 
Thus we see that in all these cases the male gives rise to two 
kinds of sperms, $ -producing or 2 -producing, while the female 
produces ova all alike and apparently all 2 -producing, as will be 
shown more clearly in the parthenogenetic cases shortly to be 
described. It is evident therefore that the male can be compared 
exactly to a Mendelian heterozygote (DR), which is heterozygous 
for maleness and femaleness ($ 5 ) with maleness dominant, and 
the female to a recessive (RR) homozygous for femaleness (22)* 
Consequently a Mendelian interpretation of sex would seem to 
be fully established in a large number of cases. Moreover, since a 
long series of species can be arranged leading from forms like Pyrro- 
clioris or Ancisa, which have a simple x-element and no y-element, to 
forms like Nezara, which have x- and y-elements almost indistin¬ 
guishable, Wilson has suggested that possibly all the sperms, at 
least in allied animals, may be differentiated with regard to sex- 
potentialities, although cytologically they are all alike. This theory 
of sex is supported in a remarkable manner by the phenomena 
exhibited by the chromosomes in the maturation of ova, and in 
the spermatogenesis in animals such as Ants, Bees, Hornets, the 
green flies (Aphids) and the vine pest, Phylloxera, which reproduce 
both sexually and asexually (i.e., parthenogetically). 
It is well-known that drone (i.e., $) bees are produced par- 
thenogenetically by the females, and that females, whether workers 
or queens, are produced only from fertilised eggs. The females of 
Aphids and Phylloxera, however, produce both males and females 
parthenogenetically, but here again fertilised eggs always develop 
into females. These facts, naturally enough, were urged against the 
views we have just discussed. But when the cytological phe¬ 
nomena in gametogenesis had been worked out, the apparently 
contradictory facts were ultimately brought into line. Indeed it 
